1. Field of the Invention
The present invention relates to methods for pre-shaping plastic films that are used in co-molding processes to cover plastic substrates and to articles made by these methods.
2. Description of the Prior Art
A variety of injection molded parts are made and used for automobile body and trim parts. For example, bumpers, spoilers, body panels, doors, filler panels, wheel covers, dashboards, arm rests and other parts are commonly made by the injection molding of thermoplastic materials.
In order to provide a painted or other decorative surface for these parts, film lamination techniques are commonly employed. A paint film laminate is insert molded or as it is sometimes referred to, co-molded, with the desired thermoplastic to fuse the film over the injection molded substrate. The resulting injection molded film-plastic part is ready for assembly without subsequent painting.
The paint film laminate used in these insert molding techniques may comprise a backing sheet of about 0.020 inch (0.5 mm) in thickness to which paint, other pigment containing, or clear layers are adhered. Typically, the backing sheet comprises an extruded thermoplastic sheet. The paint or pigment layer may contain colored pigments or reflective flake pigments such as aluminum or mica flakes to provide for example a metallic finish.
The paint film may consist of a monocoat, a clear coat over a base coat or a clear coat and a base coat with interposed print or design. The paint film, including base coat, clear coat and print or design, if desired, may range from about 0.5-4 mil. (13-100 .mu.m) in thickness.
Laminated paint films are well known in the art and are available, for example, from Avery Dennison Decorative Films Div. of Schererville, Ind., or Decorative Products of Charlotte, N.C. For example, laminated paint films are detailed in U.S. Pat. No. 5,514,427. The entire disclosure of this patent is incorporated by reference herein. The films are typically provided in a roll, unwound and then "preformed" to a size and shape approximating that of the final injection molded film-plastic part. The preforming process may comprise compressing and heating the film within a mold cavity to impart the desired basic shape to the film.
Preforming may also be accomplished by heating the film and then shaping it over a pattern block which generally corresponds to the size and shape of the finished injection molded part. A vacuum may be drawn from a plenum communicating with air channel means in the pattern block to draw the paint film over the pattern block and conform it to the desired shape.
The preform is next usually trimmed to a proper size and placed along the cavity side of an injection mold with the painted side or "show" side thereof facing the mold cavity surface. In some instances, the preform may be placed along the core side of the mold. The mold is then clamped and the desired molten resin is injected into the mold cavity. Heat and pressure conditions in the mold partially melt the backing sheet and a melt bonding or fusion of the injected resin and the backing sheet of the film occur. Injection molds used for these processes are rear or edge gated so that the molten resin is directed along the backside of the film.
Techniques for preforming paint film laminates and insert molding film-plastic parts are disclosed in U.S. Pat. No. 5,599,608. The disclosure of this patent is incorporated herein by reference.
Although the prior art lamination techniques provide significant advantage, they are not without problem. One problem is a lack of gloss consistency on the show surface of the film laminate after it is fused to the plastic part. For example, when the paint film laminate is preformed to approximate the shape of a part having a surface discontinuity such as a boss, recess, aperture or cut out portion, the portion of the film in the neighborhood of the surface discontinuity is deformed (e.g., elongated) more than the surrounding portion of the film. This adversely affects gloss uniformity of the show surface. The paint coating in the areas surrounding such discontinuity is duller than the other show surfaces. The result is that a co-molded paint film covered plastic part is formed wherein there is a substantial difference in gloss on the show side of the part.
Accordingly, there remains a need in the art to improve on the existing methods for preforming plastic film members prior to co-molding thereof with the requisite plastic so as to provide more uniform gloss characteristics on the show side of co-molded plastic parts.